In the past, rock crusher designers have endeavored to improve the ease of operating and adjustment of jaw-type rock crushers. While many improvements have been made to reduce the effort associated with adjusting such crushers, adjustment of such crushers often remains a non-trivial task. Most jaw-type crushers usually have a fixed jaw and a large heavy movable jaw known as a pitman which is driven by an eccentric shaft which causes the pitman to move along a non-circular path.
Typically, the bottom of the pitman is supported by a piece of metal called the toggle plate. It serves the purpose of allowing, within limits, the bottom of the pitman to move up and down with the motion of the eccentric shaft, as well as serve as an overload protection mechanism for the entire crusher. Should a piece of non-crushable material such as a steel loader tooth (sometimes called “tramp iron”) enter the jaw of the crusher and be larger than the maximum allowed size for passing through the jaw (the output material size setting), it can't be crushed nor pass through the jaw. In this case, the toggle plate is designed to collapse and prevent further damage to the rest of the crusher.
Adjustment of the location of the toggle plate effectively adjusts the output material size setting. A common approach to adjusting the location of the toggle plate is to use a pair of reversed overlapping wedges which are hydraulically actuated so that when maximum overlap occurs, the output material size setting is at a minimum.
A tension rod is typically included to maintain contact between the pitman and the movable toggle plate in an effort to reduce wear on these components.
These tension rods have various types of construction. One type of tension rod used in the past has been a spring coupled to a threaded rod and nut combination. Adjustment of the nut can adjust the tension applied. Others have used hydraulic cylinders with an accumulator to essentially effectuate an adjustable “hydraulic spring.” Other hybrid designs have used hydraulic or pneumatic power to maintain a constant pressure applied to a spring.
While these and other types of tension rods have improved the operation of a jaw crusher, they do have several drawbacks.
First of all, all types of spring-loaded tension rods generally make it more difficult to manipulate the overlapping wedges due to the high spring forces.
The hydraulic cylinder with an accumulator often results in leakage at the hydraulic seal owing to the very rapid movement of the tension rod.
The hybrid types of tension rods may require a manual release of the hydraulic pressure therein to reduce the pressure, thereby making it easier to manipulate the overlapping wedges.
Consequently, there exists a need for improved methods and systems for tensioning a toggle plate and a pitman in an efficient manner.